Does fast eating really lead to obesity

Eating late really makes you fat?

"Eat breakfast like an emperor, lunch like a king and dinner like a beggar" - you are probably familiar with this saying. It originally dates from a time when people had to do hard work in the fields and needed enough energy to do it. But even today, some nutritionists advise skipping dinner on diets to make it easier to lose weight. What is it about this nutritional myth?

Rising obesity rate as a health risk

Overweight and obesity are one of the greatest health problems on our planet today. The overweight rate has almost tripled since 1975 - the WHO speaks of 1.9 billion overweight adults¹ worldwide. The Austrian Nutrition Report 2017 is also clear: 41 percent of adults in the Austrian population are overweight or obese, with higher age groups and more men being affected by it². Since overweight and obesity can lead to various metabolic secondary diseases such as type II diabetes, high blood pressure and cardiovascular diseases, today's science is concerned with them³.

Changed rhythm of life and obesity

What are the reasons for the rise in obesity? The fact is that people today eat more calories on average than they used to, but exercise less and less. If the body absorbs more calories than it consumes, excess energy is initially stored in the form of glycogen - consisting of many glucose units - in liver and muscle cells. If these stores are full and food is still being consumed, the excess is stored in fat cells in the form of triglycerides (fats). Experts agree that an excessively high calorie intake and insufficient energy consumption due to a lack of exercise alone cannot explain the extent of the global obesity epidemic.

More and more studies indicate that not only what we eat, but also the time of day - i.e. when we eat - is decisive for an increase in body weight. The rise in obesity rates in recent decades goes hand in hand with a radical change in the way the Western population lives: the time of the last meal of the day has been pushed back more and more by working hours. With the hypothesis that there is a connection between our current rhythm of life and the obesity epidemic, what is known as chronobiology comes into play.

Coordination of meal times to the day-night rhythm

Chronobiology deals with the temporal organization and regulation of all processes of living beings. From chronobiology we now know that the internal clock not only determines our day-night rhythm, but also controls all of our important metabolic processesgänge: The daylight is perceived by special cells in the retina in the eye and the signal is sent to the internal clock, which in located in a specific region of the hypothalamus in the brain. From there, the internal clocks of the individual tissues are synchronized, including those in the liver, adipose tissue and other organs that are involved in the intake and processing of food.

While the main timer, the internal clock in the hypothalamus, is based on the light-dark cycle, the clocks in the tissues involved in the metabolism are also adjusted to the rhythm of meals. If the eating rhythm is not in harmony with the day-night rhythm, a "misalignment", i.e. an incorrect alignment between the rhythms, can occur - according to the hypothesis in chronobiology. The clocks in the tissues and organs then receive opposite signals from the main timer in the brain and from the external timer nourishment.

Studies have already shown that this is one of the main risk factors for obesity and associated diseases³. "Wrong" meal times can disrupt the internal clock and thus impair the metabolism. This in turn influences the internal clock, which can lead to secondary diseases. The idea that meal times should be in accordance with the day-night rhythm seems obvious.

Eating late makes it easier for people to be overweight

Science has long been concerned with the connection between the point in time at which food is consumed and the associated weight gain⁷. Franz Halberg, one of the decisive founders of chronobiology, was able to show in the 1970s and 1980s that not only what we eat but also when we eat plays a decisive role in the development of obesity.

Numerous nutrition experts describe omitting breakfast as an absolute no-go, but advise skipping dinner once in a while. Studies show that eating the same meal in the evening instead of in the morning is more likely to cause obesity. For example, a single 2000 calorie meal per day resulted in weight gain in the subjects who ate it in the evening. People who ate several meals a day and ate more than a third of the calories in the evening were also more likely to be overweight than those who ate more at lunchtime⁹. Both of these suggest that eating the same amount of calories later leads to obesity. However, criticism is also made of these studies: The numbers of participants used were mostly very low and the tests were each carried out within an ethnic group, so that no generally valid statement can be made⁷.

However, a research team from Italy was also able to confirm the above hypothesis in a large-scale study: Adults who ate most of their calories in the evening tended to develop obesity and associated diseases such as type II diabetes and high blood pressure, compared to test subjects who spread their calories over the whole day¹⁰.

Saturation effect at breakfast greater

Some diets have also shown that the same meal is more likely to lead to weight loss if consumed in the morning rather than in the evening⁷. It is noteworthy that postponing lunch to a later point in the day makes it difficult to lose weight, even if the same amount of calories is consumed³.

Most studies definitely agree on this, despite partly differing opinions: The satiety effect of breakfast seems to be overall greater than that of a dinner with the same number of calories⁷. As a result, this leads to eating more food in the evening, which in turn promotes weight gain in the long term. So if we eat later, we have to eat more food to really feel full.

It's hard to sleep on a full stomach

When it comes to eating in the evening, there is also a lot of discussion about when to eat the last time before going to bed. Many people find it difficult to go to bed and rest on a full stomach, and some complain of heartburn and other digestive problems. When asked about the ideal interval between the last evening meal and going to bed, a study published in 2016³ recommends that at least three hours should elapse between dinner or the last snack of the day and sleep, for the following reason: After eating food, blood sugar levels and insulin levels rise sharply. On the one hand, this provides energy that is no longer needed in the evening on the couch or later in bed, and active digestion may also keep you awake³.

In addition, in the best case scenario, the body breaks down fat at night - but a late release of insulin primarily promotes fat build-up. This is also often cited as the cause of weight gain from eating late. And even if it's just a small snack in the evening that doesn't cause digestive problems, it still has it all: Since the daily calorie requirement was usually covered by the meals of the day, extra delicacies are an additional amount of calories that are included of the energy demand is actually not needed and is therefore "deposited". It is interesting that this unhealthy habit can even occur in a particularly pronounced form as an eating disorder. In the case of "Night Eating Syndrome" (NES), that is, eating at night, the sick eat the majority of their food in the evening or at night. They show a particularly strongly delayed eating pattern compared to their sleep rhythm. NES correlates significantly with an increased body mass index³.


As is so often the case in the field of nutrition, opinions and study results also differ on the question of whether or not eating late makes you fat. A number of studies also cited here show that meals consumed late make obesity. However, whether the studies were carried out correctly - for example with regard to the sample size - is sometimes doubted. One thing should not be ignored in general with this topic: The genetic predisposition also determines how well one's own metabolism can utilize food and how strongly an individual tends to become overweight.

In times when everything is available anytime and anywhere, and we no longer have to adapt our rhythm to daylight, we should also consider: Our "natural" metabolism is in principle in harmony with the change between day and night. If no final statement can be made here, at least one thing is certain: When it comes to the therapy of overweight and obesity and the effectiveness of various diets, nutrition experts generally advise against eating too late. And: "Breakfast like an emperor" also seems to be important, since the overall satiety effect is greater than that of a dinner with the same number of calories. Of course, the total amount of energy consumed should always be taken into account. (Julia Auer, June 28, 2018)

Julia Auer is a geneticist and did research in Vienna and Lübeck in the field of chronobiology. She has been working at Open Science - Life Sciences in Dialogue in science communication since 2017. She is one of the bloggers who write the articles for the Hungry for Science blog from Open Science as a "better know".

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⁸ Halberg F .: Some aspects of the chronobiology of nutrition: more work is needed on "when to eat" (1989).

⁹ Wang JB, Patterson RE, Ang A. et al .: Timing of energy intake during the day is associated with the risk of obesity in adults (2014).

¹⁰ Bo S., Musso G., Beccuti G. et al .: Consuming More of Daily Caloric Intake at Dinner Predisposes to Obesity. A 6-Year Population-Based Prospective Cohort Study (2014).

11 Zahid A .: Genetic Aspects of Human Obesity: A Review (2003). Journal Of Pakistan Medical Association.

12 Larder R., Lim CT and Coll AP. Genetic aspects of human obesity (2014).